The present invention relates to an image data processing device, especially to a device to correct an inclination of an image, and more particularly, to an inclination correction device which can correct an inclination of an image that is caused when the image is inclined to an image reading means when being read in the course of reading and can output a non-inclined image, and to an image reading apparatus having therein the inclination correction device. The invention can be used for a scanner, a facsimile machine and a digital copying machine.
As a method of processing to correct an inclination of an original document for forming a non-inclined image by correcting image data obtained through reading an inclined original document in the course of image reading by scanning the original document in the main scanning direction and in the sub-scanning direction, there is one wherein image data are taken as an aggregate of linear data in the main scanning direction or an aggregate of linear data in the sub-scanning direction, and a shifting processing which shifts in the main scanning direction the linear data in the main scanning direction constituting an image, and a shifting processing which shifts in the sub-scanning direction the linear data in the sub-scanning direction are combined.
Incidentally, in the following explanation, the main scanning direction is expressed as a lateral direction, processing to shift in the main scanning direction is expressed as lateral shifting processing, while the sub-scanning direction is expressed as a longitudinal direction, processing to shift in the sub-scanning direction is expressed as longitudinal shifting.
The applicant of the invention has filed an application of TOKKAIHEI NO. 10-336425 concerning how to correct an inclination of an image through the shifting processing mentioned above.
Since processing is conducted for each linear data in this method, it is possible to limit the circuit size to be relatively small, compared with a method to conduct processing for each pixel like affine transformation, and high speed processing is expected.
Though a quantity of shifting in shifting processing is originally expressed by real numbers, actual shifting is conducted on a unit of a pixel, namely on a unit of an integer. Eventually, an error which is smaller than a decimal fraction is generated. Accordingly, there has been a problem of deterioration of image quality, including that fine lines are serrated.
For the image data transmitted on a serial basis, a memory for plural lines corresponding to the inclination angle is needed in the aforesaid shifting processing, and a capacity of the memory corresponds to the product of the number of pixels for plural lines and the number of bits of the pixel. When an 8-bit pixel is assumed, necessary memory capacity is made greater, resulting in a problem in practical use.
Therefore, an object of the invention is to solve the problems stated above in the inclination correction processing for an original document, and to provide an inclination correction device and an image reading apparatus wherein deterioration of image quality is prevented and an increase of the memory capacity is controlled.
The objects of the invention mentioned above can be attained by either one of the following structures.
Structure 1
An inclination correction device for correcting an inclination of an image caused when the image is read while it is inclined from the main scanning direction in an image reading apparatus which scans the image in the main scanning direction and in the sub-scanning direction, by shifting processing to shift the image in at least one direction, wherein there is provided an interpolation processing means which corrects an error that is smaller than a pixel unit and is caused in the shifting processing through interpolation processing.
Structure 2
An inclination correction device for processing image data inputted on a serial basis and for correcting an inclination of an image caused when the image is read while it is inclined from the main scanning direction in an image reading apparatus which scans the image in the main scanning direction and in the sub-scanning direction, by shifting the image at least in the sub-scanning direction, wherein there is provided a multiple coding means for reducing the bit number of a pixel value which operates prior to the shifting processing for shifting the image in the sub-scanning direction.
Structure 3
An image reading apparatus having therein an image reading means for reading an image of an original document by scanning the image in the main scanning direction and in the sub-scanning direction and an image processing means for processing image data inputted from the image reading means and thereby for outputting image data for image forming, wherein the image processing means has therein an inclination correction means for correcting an inclination of an image through shifting processing to shift an image at least in one direction, and the inclination correction means has an interpolation processing means for correcting an error that is smaller than a pixel unit and is caused in the shifting processing.
Structure 4
An image reading apparatus having therein an image reading means for reading an image of an original document by scanning the image in the main scanning direction and in the sub-scanning direction and an image processing means for processing image data inputted from the image reading means on a serial basis and thereby for outputting image data for image forming, wherein the image processing means has therein an inclination correction means for conducting shifting processing to shift an image inclination at least in the sub-scanning direction, and the inclination correction means has a multiple coding means for reducing the bit number of a pixel value, and multiple coding processing by the multiple coding means is conducted prior to the shifting processing for shifting an image in the sub-scanning direction.